Such a process is known from, e.g., WO-A 2006/020083. This document describes a process wherein methanol is converted to dimethylether in the presence of a first catalyst. Dimethylether is subsequently converted to light olefins and water in the presence of a second catalyst. In one embodiment the methanol is contacted with the first catalyst to convert methanol into dimethylether and water. Then unreacted methanol, dimethylether and water are combined with a recycle stream to form a combined stream. The combined stream is then separated into a first overhead stream comprising dimethylether and methanol and a first bottoms stream comprising a weight majority of water. The first overhead stream with dimethylether and methanol is subsequently contacted with the second catalyst to effect the conversion to light olefins and water. Finally, a portion of the water from the conversion into olefins is removed and used as the recycle stream and combined with the stream comprising dimethylether, unreacted methanol and water. Although the known process makes an attempt to integrate the dimethylether preparation and the olefin production, the process does not make effective use of the exothermic nature of the reactions.
In EP-B 88494 a process is described in which methanol is converted to dimethylether and water and, subsequently, the dimethylether is converted to olefins. The document describes that both the dimethylether preparation and the olefin production are exothermic. Therefore it is proposed to conduct the olefin production in several reaction stages, wherein use is made of interstage cooling. Moreover, it is suggested that the product from the dimethylether preparation is subjected to indirect heat exchange with, e.g., water or the methanol reactant. In the process according to EP-B 88494 water that is formed at the dimethylether preparation is only partly separated and removed after the conversion of dimethylether to olefins, together with the water produced during the conversion of dimethylether. That means that water formed at the dimethylether preparation is present at the olefin production from dimethylether and methanol. Therefore the streams through the reactions for the olefin production are unnecessarily large.
US 2006/0020155, US2007/0155999 and US2007/0203380 all disclose processes for converting synthesis gas via dimethylether to light olefins. The documents do not consider optimization of the heat integration in a process for converting an alkylalkohol stream via dialkylether to an olefinic product, in particular not starting from a relatively pure alkylalkohol stream not containing unreacted synthesis gas.
The present invention has the objective to reduce the amounts of process streams at the conversion of dimethylether to olefins, whilst improving the heat integration between the dimethylether preparation and the olefins manufacture.